In the current state of the art, the production of hollow fibers is greatly hindered by the required extrusion process using an annular die, which makes the production of fibers having a small cross-sectional area very difficult. Such processes are also sensitive to the polymer composition being extruded, limiting the variety of compositions available for practice. Hollow fiber production is further limited because hollow fibers are especially prone to breakage, rupture, or other defects during any draw-down (spinning) process, which further limits the size, geometries, and other physical properties typically achieved during a conventional spinning process.
Another limitation of the current art is the control (or lack thereof) of the polymer molecule orientation in the final hollow fiber. In conventional hollow fiber production, the polymer molecules become oriented, at least partially, in the longitudinal direction by the extrusion and/or spinning process. While this may benefit the strength of the fiber in the longitudinal direction, it actually can degrade other properties such as its resistance to collapse, crushing, fraying, crimping or other failure modes of the fiber. Thus, a technique capable of providing or imparting some degree of radial orientation to the polymer molecules in the shell wall of the fiber is desirable. Such radial orientation of the polymer chains is not currently achievable in the current art, yet would provide the hollow fibers with heretofore unattainable properties, even if only partial radial orientation could be achieved.